Scab is very hard to control in organic fruit cultivation. But there is hope. Applied Plant Research (PPO) is testing new products that appear to be effective.
Organic fruit growers in the Netherlands have few possibilities to control scab; few biological scabicides are available. Organic growers can also combat scab by preventing the disease to survive winter. The fungus survives on dropped leaf material and does not survive without leaves. But only a small amount of leaf material is required for the fungus to survive and hit again in spring.
Yucca and baking powder against scab
The researchers of PPO therefore started searching for alternatives. They searched the literature and investigated experiences abroad. This took them to several products, such as a soapy substance from the yucca plant and baking powder (bicarbonate). They tested these products and both were found to be effective. Disadvantage of the yucca extract is that it is not permitted as crop protection product; bicarbonate is allowed.
In a follow-up step the scientists tested bicarbonate under field conditions. They discovered that the powder has a preventative effect: it prevents the fungus from infesting the trees. And it is even more effective shortly after infestation. The only disadvantage of bicarbonate is a slight russeting of the fruit skin.
More new products
In new research the scientists want to investigate how skin russeting can be reduced. And they continue their search for other ways to control the fungus. Apart from the products mentioned above this involves biological control agents such as Cladosporium cladosporioides H39. This so-called antagonistic fungus has been developed by Plant Research International, also part of Wageningen UR.